1. Field of the Invention
The present invention relates to a lead frame having at least two leads and usable for resin-sealing a semiconductor chip, a mold for producing a resin-sealed semiconductor device using such a lead frame, a resin-sealed semiconductor device using such a lead frame, and a method for producing a resin-sealed semiconductor device using such a lead frame.
2. Description of the Related Art
Recently, semiconductor devices have an increased number of pins used for electrodes in accordance with an increase in complexity of the circuit structure mounted therein, the incorporation of various devices into a system, and the diversification of uses. The withstanding voltage characteristic (hereinafter, referred to as the "withstanding voltage") of semiconductor devices has been increased. Therefore, a significantly high voltage may be applied between adjacent leads of a semiconductor device. Accordingly, the distance between such adjacent leads needs to be increased. For example, the minimum possible distance between two adjacent leads is generally considered to be 5 mm in the case of a semiconductor device having a withstanding voltage of 600 V. Such a trend in development requires development of special packages for semiconductor devices and new production facilities, which results in a higher cost for the semiconductor devices.
As one proposal for coping with the abovementioned development trend, common use of components such as packages and lead frames for semiconductors having different specifications have been researched.
FIG. 29 is a plan view of a conventional lead frame 1 for resin-sealing a semiconductor chip 2. The lead frame 1 includes five leads, namely, two leads 1a, two leads 1b and one lead 1c.
The semiconductor chip 2 is resin-sealed using the lead frame 1 in the following manner.
The semiconductor chip 2 is bonded on a die-mount portion 1d of the lead frame 1, and the semiconductor chip 2 is connected to the leads 1a via thin metal wires 3. The semiconductor chip 2 and the lead frame 1 are resin-sealed in a resin-seal body 6 except for the outer ends of the five leads 1a, 1b and 1c. Then, the lead 1c which is not connected to the semiconductor chip 2 is cut along an outer peripheral surface of the resin-seal body 6 by appropriate machining.
Conventionally, a common lead frame is used for resin-sealing semiconductor chips having different manners of wire connection in order to allow for use of a common mold. After the semiconductor chip is resin-sealed, the unnecessary lead (such as 1c) which is not connected to the semiconductor chip is cut off in an appropriate manner. Consequently, circuits having complicated structures are produced with relative ease.
However, in the manner of resin-sealing described with reference to FIG. 29, after the unnecessary lead 1c is cut off, a part 1c' thereof is left on the outer peripheral surface of the resin-seal body 6. During the flow-soldering or dip-soldering performed subsequent to the resin-seal, solder H adheres to the part 1c'. This causes the part 1c' to be a separate conductive part existing between the two respective leads 1a, resulting in potential electric connection of the two leads 1a to each other. When such a phenomenon (the solder adherence) gets too large, the withstanding voltage of the semiconductor device is lowered and sometimes the device does not function.
As the number of pins connected to a semiconductor chip increases, the distance between two adjacent leads is decreased. As the withstanding voltage of a semiconductor device rises, the voltage applied between the leads also rises. In order to cope with such a trend, a sufficient withstanding voltage should be obtained between the shortened lead distance.
In order to prevent the withstanding voltage between leads from decreasing, a lead frame and a mold specially used for each of various types of semiconductor devices are used. This raises the cost of the molds and also increases the number of mold replacements, thus raising the production cost of the semiconductor devices.